Sound ranging distance measuring system



April 4, 1950 R. A. F-RYKLUND EI'AL 2,502,933

SOUND RANGING DISTANCE MEASURING SYSTEM 3 Sheets-Sheet 1 Filed May 21, 1947 INVENTORS FRYKLUND JOHN M. BEEBE T RNEY ROBE RT A.

THEIR AAA 5&3 3.2 581 W wQED O OF A April 4, 1950 Filed May 21, 1947 TO VOLTAGE REGULATED SUPPLY- l VOLTAGE R. A. FRYKLUND ETAL SOUND RANGING DISTANCE MEASURING SYSTEM 3 Sheets-Sheet 3 was FIG. l5 T TO VOLTAGE REGULATED SUPPLY 49 T0 ANODE OF SAMPLER TUBE 45 ROBERT JOHN THEIR A TORNEY Patented Apr. 4, 1950 SOUND HANGING DISTANCE MEASURING SYSTEM Robert A. Frykiund, Somerville, and John N.

Beebe, West Roxbury, Mam, assign theon Manufacturing Company, a

of Delaware on to Baycorporation Application May 21, 1947, Serial No. 749,426

The present invention relates in general to apparatus for measuring the distance to a surface by the transmission of compressional wave energy toward the surface, and the reception of compressional wave energy reflected from the surface, and in particular to such apparatus as used for determining the depth of a body of water.

It is an object of the. present invention to provide an improved apparatus for water depth sounding of the type wherein an ordinary electrical meter may be employed to indicate the depth.

It is another object to provide such an apparatus wherein a pulse which triggers the transmitted pulse of energy is employed to advantage to provide'a. zero standard for the meter, and which cannot provide a false depth, or zero reading, but always provides a reliable standard.

Additional objects of the invention are to provide such an apparatus wherein, if no echoes are received, the meter reading drops to zero or a minimum, and wherein the meter .is maintained sensitive only to the first echo returned, and is rendered insensitive to any second, third, or other spurious echoes that may return.

Another object is to provide a reliable direct reading water depth measuring apparatus.

Still another object is to minimize the response of the indicating meter to spurious signals due to reverberations, mechanical ringing" of the transducer, or ringing of the tuned circuit.

It is alsoan object of the invention to provide a depth indicator of the above described kind which is relatively light in weight, compact, portable, and inexpensive, and can be operated for long periods of time from an ordinary low voltage battery.

The foregoing and other objects and features of th present invention will be best understood from the following description of a circuit embodying the invention particularly for the purpose of water depth measurement, reference being had to the accompanying drawings wherein:

Fig. 1 is a schematic representation of a circuit embodying the invention;

Figs. 2 to 11 inclusive are graphs illustrating the operation of the circuit of Fig. 1;

Fig. 12 is a schematic representation of a vacuum tube voltmeter that may be used with the circult of Fig. 1;

Fig. 13 is schematic representation of a modification of the sweep generator shown in Fig. 1;

Fig. 14 is a graph illustrating the operation of the device shown in Fig. 13;

Fig. 15 is a schematic representation of another modiflcation of the sweep generator; and

Fig. 16 is a fractional view of a synchronizing pulse generator that may be used with the modiflcation of Fig. 15.

Referring now to Fig. 1, a gaseous discharge 9 cam. (Cl. 177-386) 2 tube I, for example a Thyratron, and its associated circuit components comprise a saw-tooth wave generator. This tube and its circuit are used for many purposes: to provide a linear time base, to control the keying of a pulse generator, and to provide a zero standard for an indicating meter, as will be described below. A voltage regulated power supply (not shown) is preferably used to supply the plate voltage for the tube through a variable plate resistor 3. A condenser 2, the charging and discharging of which provides the saw-tooth voltage output, is connected from the plate of the gas tube I to ground. With the application of plate voltage to the gas tube I, the condenser-.2 is charged at a-rate determined by the product of the resistance of the plate circuit resistor 3 and the capacitance of the condenser 2. The polarity of the charge is such that a positive charge is built up on the anode of the gas tube, to which the condenser is connected. In order to obtain a nearly linear charging curve, the grid bias of the gas tube l is so regulated that the tube fires before the condenser 2 is fully charged, and only a, substantially linear portion'of the charging curve is utilized. A voltage divider consisting of the resisters 6 and 5 connected from 13+ to ground, to the. junction of which the cathode of the gas tube is connected, determines the grid bias of the tube. A cathode by-pass capacitor 6 is connected across the cathode resistor 5. The value of the resistors 4 and 5 may be so chosen that the cathode has a predetermined positive potential with respect to the grid potential (the grid may be grounded as shown in Fig. 1), and this causes the tube to fire at the desired point on the charging curve of the condenser. For example if the bias is adjusted so that the gaseous discharge tube I, is fired by a plate voltage E: which is less than the highest voltage E-available from the B+ supply, as represented in Figure 2, a substantially linear saw-tooth pattern is obtained. The upward sloping portion C (from line a to line b) of this voltage pattern, appearing on the plate of the tube is used in the circuit as a time base in a manner which will be described below. The lowest voltage Ea shown in Fig. 2 is the extinction voltage of the tube with this bias condition.

In Fig. 2, time is represented along a horizontal axis, the start of a time base sweep C occurring at a, c, and e, and ending at b, d, and 1 respectively, while return voltage D occurs between trate the time relationship of the waves. Voltage or current is represented in all cases alon the vertical axis. I

A transformer I is connected with its primary winding in series in the cathode circuit of the gas tube I. This transformer has low inductance in its primary coil circuit and is designed so that its core will not saturate, as used in the saw-tooth generator circuit. It performs the function of a differentiating transformer as follows. =During the time (a to b in Fig. 2) the condenser 2 is charging and the tube I is cut on, no current flows in the gas tube I, and hence through the primary winding of the' transformer 1. However, during the time the tube is conducting (b to c in Fig. 2), while the condenser 2 is being discharged, there is a surge of current through the tube, and consequently through the primary winding of the transformer, the approximate wave form of which is shown in Fig. 3. The transformer 1 then produces negative and positive pips in its secondary winding. having a wellknown form generally as shown in Fig. 4. The transformer is so connected to the tube 9 that follows that a positive pip is produced at the end of every discharge of the condenser 2, or, inv other words, at the beginning of every charging p riod of the condenser 2. This positive pip is used to control the tube 9, which is in a. blocking oscillator circuit and in turn causes a pulse of compressional wave energy to be projected by a transducer 7 8 at the instant the condenser 2 starts to charge, that is, at the beginning of each time base sweep C. The time taken for the condenser 2 to discharge, namely time b to c, d to e, or f to g, is employed to advantage to provide the positive pips shown in Fig. 4 at the beginning of the time bases C, rather than at the ends thereof. As will be seen, this provides for a reliable stable zero" standard for the indicating meter.

The output of the differentiating transformer 1, consisting of the negative and positive pips of Fig. 4, is impressed on the control grid of the electron discharge tube 9 through a coupling condenser i and an inductance ll connected together in series. Plate voltage is supplied to the tube 9 through a plate resistor i2, and a tuned circuit comprising an inductance l3 and a capacitance I4 connected together in parallel. This circuit may be tuned to any desired frequency, for example 45 kilocycles. The coil is is coupled to the inductance II in the grid circuit of the tube, providin plate to grid ,feedback which establishes oscillation as the frequency of the tuned circuit. The blocking oscillator circuit is normally biased to cut-off by the grid bias battery i5. However, whenever a positive pip from the transformer I is impressed on the grid of the tube 9, oscillation is initiated. The

tube then continues to oscillate until it is blocked by the voltage built up on the coupling condenser lil by the flow of current through the grid resistor It. By suitably choosing the values of the coupling condenser W and the grid resistor it, the time required for the oscillator to block may be adjusted so that the oscillator produces a short (for example about millisecond) pulse of oscillating voltage for each positive pip that appears on the control grid of the tube 9, as shown in Fig. 5. An additional condenser 70 may be connected across the battery l5 and grid resistor it for the purpose of lengthening the oscillation period. The oscillating electric pulses are transformed to compressional wave energy the instant the condenser 2 of the saw-tooth wave generator I has just begun to recharge, a pulse of oscillating energy is produced by the blocking oscillator, which pulse is propagated into space as compressional wave energy by the transducer 8. Simultaneously, the same oscillator pulse, which will be called a direct pulse," is also transmitted to the subsequent amplifier stages 20 and 2| through a coupling condenser l8. Compressional waves received by the transducer 8 due to reflection of the transmitted pulses of compressional wave energy from an object in their path are converted to electrical energy by the transducer 8 and coupled into the amplifier circuit through the tuned circuit inductance It. This energy will be called the reflected pulses, and passes throughthe amplifier coupling condenser I8 to the amplifier stages just as the direct pulses" do. The same tuned circuit is used for both the transmit and receive functions.

Two stages of amplification 20 and 2| are em-' ployed in Fig. 1. The tubes used may be 680'! or any other suitable type. The first coupling resistor I9 is a limiting resistor to prevent overloading the first tube 20 on strong direct signals. Both amplifier tubes are operated as time varied gain amplifiers. When a strong signal is impressed on the control grids of these tubes, such as the direct pulse, the tubes draw sufiicient grid current to charge the coupling condensers l8 and 22, the polarity of the charge being such that a negative charge appears on the respective grids, which reduces the gain of the amplifiers. This self-induced grid bias is then permitted to leak oil! through grid leak resistors 23 and 24 respectively so that in a desired interval of time the amplifiers have regained full sensitivity. The purpose of this is to decrease the sensitivity of the amplifiers directly after a direct pulse is impressed on them so that they will be insensitive to the ,hash following a direct pulse. This hash results from mechanical ringing of the transducer 8 after a pulse had been transmitted and is due also tothe energy that is stored in the tuned circuit l3 and M of the oscillator. As will be understood later, the presence of this "hash after the direct signal must be compensated for to prevent spurious readings in the meter. Using two stages of time varied gain has this effect since the gain of the amplifiers is so decreased directly after a direct pulse that the circuit is rendered insensitive to the hash, while suificient amplifler sensitivity is retained to amplify echoes that may be received. The use of a single tuned circuit, the inductor l3 and capacitor I 4, for both the transmit and receive function is thus made feasible.

The resistance-capacitance values of the resistor-condenser combinations I8, 23 and 22, 24 which determine the time required for the amplifiers 20 and 2| to regain full sensitivity after a strong signal has been impressed on them are so chosen that the amplifiers are not rendered insensitive to the reflected pulses. The strength of the reflected pulses picked up by the transducer t is inversely proportional to the square of the distance to the reflecting surface; the shorter the distance, the stronger the reflected pulse and the greater the distance, the weaker the reflected pulse. Consequently any reflected pulse received by the transducer 8 which is coupled to the in a depth of water so shallow that it is impressed on the amplifier during the time "hash from a direct signal still appears therein will have a strength considerably greater than the hash." Therefore by the proper choice of circuit constants, the time varied gain effect is made such that the amplifiers will be insensitive to hash" but will be sensitive to any reflected pulses picked up while "hash is still existent. Furthermore, the circuit is made such that the amplifier sensitivity is restored at a rate greater than the rate at which the reflected signal strength decreases.

The amplified signals produced on the plate of the second amplifier tube 2| are represented in Fig. 6. The direct signals are usually so strong that either or both amplifier stages may overload,

resulting in the clipped or limited form 25 shown.

Due to the effect of the time varied gain, the "hash of Fig. 5 has been virtually eliminated. It may also be observed that another efiectof the time varied gain is to cause the echoes 26 from whatever distance received to have a more constant value.

The signals represented by Fig. ii are impressed on the grid of a detector tube 21 through a coupling condenser 28. The detector tube 21 is operated preferably as an infinite impedance detector, and'the cathode resistor 29 is accordingly sufiiciently large so that the tube is self-biased nearly to plate current cut-off. The cathode bypass condenser 30 and the resistor 29 together in the cathode circuit of the detector comprise a resistance-capacitance filter which further filters out "hash that may remain after the direct signal. The resistor 29 may for this purpose have a value of, for example, 150,000 ohms, and the capacitor a value of 0.02 microfarad. The detector tube 21 being a rectifier, only the positive voltage portion of the signals shown in Fig. 6 is eifective. The capacitor 30 being small, it is quickly charged to the full available voltage when the pulses 25 and 26 are applied, and then discharges slowly through the resistor 29, so that th voltage wave of the output'of the detector tube 21 is as shown in Fig. '7. The slow discharge of the capacitor 30 renders the detectoroutput insensitive to any remaining hash after the direct signal, but the discharge is fast enough so that an echo is detected. The sharp rise of the echo pulse is used to control the stages that follow, as will be explained, and it is desirable that the first sharp rise after a direct pulse be that of the first echo.

The output of the detector is impressed on the grid of a gaseous discharge tube 3|, which may be a Thyratron, through a coupling condenser 32. This tube 3| is normally biased just below the firing point, as by a battery 33. The cathode is connected to ground through a cathode resistor 35 and a switch tube 34, which may be a high vacuum triode.

A sufliciently high plate voltage is supplied to the switch tube 34 through the gas tube 3| and the cathode resistor 35 to render the switch tube 34 conductive whenever the gas tube 3| is fired and the switch tube has no grid bias. On the other hand, when a negative bias voltage appears on the grid of the switch tube 34, this tube is rendered non-conductive and either cuts off the gas tube 3| if that tube is at the time conducting, or prevents it from firing if a positive pulse is simultaneously applied to the grid of the gas tube. Consequently the gas tube 3| is fired whenever there is no negative bias voltage on. the grid of the switch tube 34 and the grid of the gas tube 3| is supplied with a positive pulse from the de-= tector 21.

pling condenser 38. It will be observed that when the blocking oscillator tube 9 is blocked, this point 36 has a high positive potential. However, when the oscillator tube 9 is keyed into oscillation, the

potential at the point 36 is reduced sharply, producing a negative pip which appears on the grid of the switch tube 34. This negative pip is produced at the instant the oscillator tube 9 produces a direct pulse which, as developed above, appears on the grid of the gas tube 3| as a positive pulse. The magnitude of this negative pip is determined by the value of the switch tube grid resistor 39.

The coupling condenser 38 and the condenser II from the point 36 to ground are of such magnitudes that the negative pulse which appears on the grid of the switch tube 34 is longer in duration than the positive pulse appearing on the grid of the gas tube 3|. This negative grid pulse does not occur however when a reflected pulse is received in the transducer 8. Therefore whenever a reflected pulse is picked up the gas tube 3| is fired by the resulting positive pulse appearing on its grid and continues conducting until the oscillator tube 9 produces the next succeeding direct signal, which again causes a negative pulse to appear on the grid of the switch tube 34, cutting off both the switch tube 34 and the gas tube 3|. Thus the gas tube 3| is fired substantially at the instant a reflected pulse or echo is received and continues to remain conductive until the next direct pulse signal is produced by the oscillator tube 3. A relatively square-shaped current wave is produced in the gas tube 3|, as shown in Fig. 8. Since the gas tube 3| is conduc-- tive following the first echo received, there can be no response to second or third echoes due to multiple reflections or any other causes. The circuit responds only to the first echo received after the transmitted pulse. Inasmuch as direct pulses are produced at regular intervals, the period of time the gas tube 3| is non-conductingv is a measure of the time that elapses between the production of a direct pulse in the transducer 8 and the reception of a reflected pulse therein. This interval of time is proportional to the depth of the water in which soundings are being made. The remainder of the circuit of Fig. 1 serves to control a meter which indicates directly the depth of the water, as will now be explained.

The voltage drop across the cathode resistor 35 of the gas tube 3| is coupled through a transformer 40 to the grid of an amplifying tube 4|. This transformer 40 operates in the same manner as the saw-tooth wave generator transformer 1, providing differentiation pips at the instant when the gas tube 3i is fired and cut off, as shown in Fig. 9. The pips in Fig. 9 are relatively sharp The negative and positive pips shown in Fig. 9

" asses are pressed on the grid of the amplifier tube 6i together with the negative and positive pips (shown in Fig. 4) produced by the first trans i'ormer t, which are transmitted to the ampliiler tube 5! through a conductor 62 and an isolating condenser 72. These two trains of pips are amplified and inverted by the amplifier tube 46. A grid leak resistor it provides self-bias. An output transformer 68 couples the output of the amplifier tube M to the grid of a sampling" tube 35, and inverts the pips once again so that there appears on the grid of the sampling tube #35 an amplified series of pips having the relative appearance of those shown in Fig. 10. The centers of the positive pips of Fig. 4 and negative pips of Fig. 9 are separated slightly, for the cuton potential of the oscillator tube 9.15 somewhere up on the sloping leading edge of the positive pip. which it will be recalled, initiates the transmitted pulse which in turn initiates the cut-d of the switch tube 34. This separation has been slightly exaggerated in Fig. 10.

The grid of the sampling tube 45 is biased to cut-ofi by a bias battery 66 so that the tube operates as a detector, conducting only when positive pips are impressed on its grid. The plate voltage of the sampling tube is provided by the saw-tooth voltage output of the saw-tooth wave generator 8 through a conductor 49. The plate voltage of the tube at any given instant is therefore as represented in Fig. 2. .To simplify the explanation of the operation of the tube, Fig. 11 has been redrawn from Fig. 10 showing just the positive pips which render the sampling tube 45 conductive. Superimposed on these positive pips is the saw-tooth shaped plate voltage wave of the tube, indicated in dotted line. It will be observed that a positive pip occurs at times a, c, and e when the plate voltage is a minimum, corresponding to the time at which a direct pulse is transmitted, and also that a positive pip occurs some time after each of lines a, c, and e, when the plate voltage has built up somewhat, at a time when an echo or reflected pulse is received. During each saw-tooth, therefore, the sampling tube d conducts at two intervals, and produces rectified voltages, one a substantially constant voltage in accordance with the extinction plate voltage Ea existing at times a, c, and e, and the other a larger voltage in accordance with the plate voltage existing at the time when an echo is received. The difference between this second voltage and Ee is proportional in magnitude to the length of time required for reception of the echo of the transmitted pulse, or to the depth of the water. Rectified voltages appear across the cathode resistor d'l and cause a parallel-connected condenser 68 to charge to a voltage that is thus proportionally related to the depth of water being measured.

The importance of the time intervals b to c, d to e, and f to g, required to discharge the sawtooth generator capacitor 2, now becomes apparent. If the positive pulses of Fig. 4 occurred during the time when the time base sweep was at its maximum b, d, or I rather than at its minimum a, c, or e, the plate voltage on the sampling tube 45 would be E: during the transmitted pulse, rather than Ea. If the discharge time (D in Fig. 2) were practically instantaneous, the plate voltage On the sampling tube 45 would be apt to fluctuate between Ee and Er, so that the zero" standard voltage would not be definitelydetermined. In the present invention, however,

the "zero standard voltage is definitely maintained at Es, the minimum time base voltage. To guarantee this, the same positive pulse (Fig. 4 from the sweep generator that gates or triggers the blocking oscillator tube 9 is employed to unblock the sampler tube to obtain the "zero voltage standard. The time base sweep, transmitted pulse, and "zero" sampler tube voltage level are thus all accurately synchronized. The cathode resistor b in the sweep generator circuit aids in providing the time intervals b to c, d to e, and f to g.

The output of the circuit of Fig. 1 may be measured in a vacuum tube voltmeter, like that shown in Fig. 12, comprising two tubes at and 5%. The voltage to be measured is impressed on the rid of the first tube 6.9. The two tubes 59 and 58 have their cathodes interconnected through resistors 5! and 52 respectively, and also through a meter 53. A voltage divider comprising two series connected resistors 54 and 55 is used to maintain the bias of the second voltmeter tube 59 at a desired level such that the two tubes are balanced and no current flows through the meter when only transmitted pulses exist, but no reflected pulses are being received. The reading of the meter is then directly proportional to the voltage developed by the sampling tube 65 upon the receipt of reflected pulses. Since the magnitude of this voltage is directly proportional to the depth of the water, the meter may be calibrated to read the depth of water directly. A condenser 58 serves to filter the voltages applied to the meter so that the meter will not fluctuate unduly and so that several reflected pulses may be missed without affecting the reading.

It will be noted that a voltage regulated supply is preferred for energization of the saw-tooth voltage generator tube i,-for such a supply improves the stability of the circuit. Likewise, in Fig. 12, the vacuum tube voltmeter should be energized from the same kind of a supply for the same reason. The saw-tooth voltage generator can be further stabilized by the employment of a vibrating reed controlling arrangement as shown in Fig. 13. There both coils of the differentiating transformer E are wound on the middle leg 50 of a somewhat E-shaped magnetizable core at. A vibratable reed 62 which should be made of a magnetizable material is mounted on one outside leg 63 of the core 65, and extends over the top of the middle leg toward but not quite to the other outside leg 6d. The free end of the reed 52 is provided with a weight 65 which is prefer-- ably made of a highly magnetizable material, for example, Alnico, a highly magnetizable alloy of aluminum, cobalt, and nickel. The other outside leg 66 of the core GE is bent so that the weight 65 can pass by it when the reed oscillates, and has a coil 56 wound on it. This coil 68 is connected between the grid of the saw-tooth gem erator tube 5 and ground. The remainder of the circuit of Fig. 13 is like that shown in Fig. l.

The grid circuit coil 86 and its core leg constitute a voltage generator when the reed G2 oscillates and the weight 65 passes by the bent core leg 66, the voltage generated in the coil 66 being a pulse-like alternating voltage, oi the kind shown in Fig. 14. The reed 62 and weight 65 have a natural frequency equal to the desired pulse rate, while the relaxation oscillator or sawtooth generator I is free-running at a slightly different frequency. The current pulses (Fig. 3) that pass through the primary of the transformer 1 pulse magnetize the center leg 69 of the core 6i and the reed 62 aooaess begins to oscillate. The pulses shown in Fig. 14 are then generated and applied to the grid of the saw-tooth generator quency of the reed. Similarly, the reed 62 can lock' the tube to a frequency slightly less than that at which the tube would oscillate freely.

A simpler form of vibrating reed synchronizing arrangement is shown in Fig. 15. There the grid coil 66 and its core leg are eliminated, and the "alnico" weight 65 swings by the free end of the remaining core leg 60, being attracted thereto to start the reed 62 oscillating by the same gas tube I current pulses that start the reed in Fig. 12. The Alnico bar 65 then induces a voltage in the primary winding of the transformer I, which voltage is applied to the cathode of the tube I in such fashion as to render the cathode more negative than the grid, which may be grounded as in Fig. l, to start the tube early, or more positive than the grid toretard the fir-' ing of the tube.

The transformer I and reed 62 of Fig. 15 may be constructed as shown in Fig. 16, where the core leg 60 is bifurcated, having two arms 60A and 60B respectively. One coil IA or IE of the transformer I is wound on each arm. The Alnico weight 65 is here preferably in the form of a bar, and as it swings by the free ends of the core arms 60A and 60B, a voltage is induced in the transformer coils IA and 1B. The coil that is connected to the cathode furnishes its induced voltage thereto.

Many other modifications of the invention will occur to those skilled in the art. For example, second and third echoes may be prevented from occurring along with or close to the first echo by rendering the duration of the sweep or upward-sloping portion C of the saw-tooth wave so long that these higher order echoes will return before another energy pulse is transmitted. This is accomplished by reducing the sweep generator frequency, and hence the pulse rate. These higher order echoes then occur while the gas tube 3| is conductive, and have no effect, as explained above. If desired, separate transmitting and receiving transducers may be used in place of the singe transmitting and receiving transducer 8 used in Fig. l.

The claims that follow are intended to cover these and other modifications and equivalents of the invention and accordingly are to be given a broad interpretation commensurate with the scope of the invention within the art.

Having now described our invention, we claim:

1. An echo ranging system comprising: a sawof said return portion; means arranged to be;

triggered by said first short pulse to produce a pulse of energy for propagation into space; means to receive an echo of said propagated energy: means responsive to the reception 01 said echo for producing a second relatively short pulse substantially simultaneously with said echo; and means for measuring the difference between the voltage values of said time base portion during said first and second short pulses.

2. An echo ranging system comprising: a sawtooth wave generator for providing an electric wave having alternately a substantially linearly increasing voltage time base portion and a relatively quickly decreasing voltage return portion: means in circuit with said generator for providing a first relatively short voltage pulse substantially simultaneously with the termination of said return portion; means arranged 'to be triggered by said first short pulse to produce a pulse of energy for propagation into space, and adapted to receive an echo of said propagated energy; means responsive to thereception of said echo for producing. a second relatively short pulse substantially simultaneously with said echo; and means for measuring the diiference between the voltage values of said time base portion during said first and second short pulses.

3. An echo ranging system comprising: a sawtooth wave generator for providing an electric wave having alternately a substantially linearly increasing voltage time base portion and a relatively quickly decreasing voltage return portion; means in circuit with said generator for providing a first relatively short voltage pulse substantially simultaneously with the termination of said return portion; means arranged to be triggered by said first short pulse to produce a pulse of energy for propagation into space, and adapted to receive an echo of said propagated energy; a gaseous discharge tube arranged to be triggered into a current conductive state as a consequence of the reception of said echo; means responsive to the conductivity of said tube for producing a second relatively short pulse substantially simultaneously with said echo; and means for measuring the difi'erence between the voltage values of said time base portion during said first and sec--, ond short pulses.

4. An echo ranging system comprising: a sawtooth wave generator for providing an electric wave having alternately a substantially linearly increasing voltage time base portion and a relatively quickly decreasing voltage return portion; means in circuit with said generator for providing a first relatively short voltage pulse substantially simultaneously with the termination of said return portion; an electronic oscillator arranged to oscillate for a predetermined time interval when triggered by said first pulse; an energy transducer arranged to be energized by said oscillator to produce a pulse of energy for propagation into space, and adapted to receive an echo of said propagated energy; means including said oscillator responsive to the reception of said echo for producing a second relatively short pulse substantially simultaneously with said echo; and means for measuring the difierence between the voltage values ofsaid time base portion during said first and second short pulses.

5. An echo ranging system comprising: a sawtooth wave generator for providing an electric wave having alternately a substantially linearly increasing voltage time base portion and a relatively quickly decreasing voltage return portion; means in circuit with said generator for providing a first relatively short voltage pulse substantially simultaneously with the termination of said return portion; an electronic oscillator arranged to aeoaase triggered by said first pulse; an energy trans= ducer arranged to be energized by said oscillator to produce a pulse of energy for propagation into space; means adapted to receive an echo of said propagated energy; a gaseous discharge tube connected in said system to be triggered into a conductive state by said oscillator during the production of said pulse of energy, and during the reception of said echo; an electronic switch tube connected in series with the anode-cathode circuit of said gaseous discharge tube and connected to said oscillator to be rendered non-conductive and hence to maintain said gaseous discharge tube non-conductive during the production of said pulse of energy; means responsive to the initiation of conductivity of said gaseous discharge tube for producing a second relatively short pulse substantially simultaneously with said echo; and means for measuring the difierence between the voltage values of said time base portion during said first and second short pulses.

6. An echo ranging system comprising: a sawtooth wave generator for providing an electric wave having alternately a substantially linearly increasing voltage time base portion and a relatively quickly decreasing voltage return portion; means in circuit with said generator for providing a first relatively short voltage pulse substantially simultaneously with the termination of said return portion; an electronic oscillator arranged to oscillate for a predetermined time interval when triggered by said first pulse; an energy transducer arranged to be energized by said oscillator to produce a pulse of energy for propagation into space; means adapted to receive an echo of said propagated energy; a gaseous discharge tube connected in said system to be triggered into a non-conductive state by said oscillator during the production of said pulse of energy, and. into a conductive state during the reception of said echo, said gaseous discharge tube being rendered conductive only upon the reception of said echo, and remaining conductive thereafter until again rendered non-conductive upon the production of the next succeeding pulse of energy, whereby spurious echoes following the first received echo have no efiect upon the system; means responsive to the initiation of conductivity of said gaseous discharge tube for producing a second relatively short pulse substantially simultaneously with said echo; and means for measuring the difierence between the voltage values of said time base portion during said first and second short pulses.

'7. In an echo ranging system wherein an oscillatory circuit is energized to produce pulses of oscillatory energy; a detector connected to said oscillatory circuit to rectify said pulses; said detector comprising an input circuit and an output circuit; said output circuit having current rectifying means therein, the conductivity oi in presence of a, pulse in said input circuit, but discharges slowly through said resistance means when said current rectifying means is rendered non-conductive, whereby minor fluctuating signals following said pulse due to spurious ringing of said oscillatory circuit and similar causes are not detected by said detector; the discharge of said capacitance means being however sufiiciently fast so that a succeeding pulse which is of greater magnitude than said minor signals is detected.

8. An echo ranging system comprising, in combination with means for transmitting and receiving energy pulses, a gaseous discharge tube and a vacuum type tube having their anodeoathode paths serially connected, means biasing said gaseous tube to a normally non-conductive state, means biasing said vacuum type tube to a normally conductive state, means responsive to the production of a transmitted energy pulse for momentarily biasing said vacuum tube to a nonconductive state, and means responsive to the receipt of an energy pulse for biasing said gaseous tube to a conductive state.

9. An echo ranging system comprising, in combination with means for transmitting and receiving energy pulses, a gaseous discharge tube having anode, cathode, and control grid electrodes, a vacuum type tube having anode, cathode, and control grid electrodes, means connecting said gaseous tube cathode to said vacuum tube anode, means normally biasing said gaseous tube control grid to a non-conductive level with respect to said gaseous tube cathode, means normally biasing said vacuum tube control grid to a conductive level with respect to said vacuum tube cathode, means responsive to the production of a transmitted energy pulse for momentarily biasing said vacuum tube to a non-conductive state, and means responsive to the receipt of an energy pulse for biasing said gaseous tube to a conductive state.

ROBmT A. FRUND.

JOHN N.

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